This invention relates to the field of hand held rotary tools and related accessories.
Hand held rotary tools are widely used by many people, including craftspeople, homeowners, and artists. These rotary tools typically include an outer housing designed to be easily held within a human hand. The housing retains an electric motor which is operable to drive a rotatable chuck of the rotary tool. An accessory may be releasably secured to the chuck thereby enabling the rotary tool to rotatably drive the accessory.
The widespread use of hand held rotary tools is a result, in part, of the wide variety of accessories that may be used with the tools. The accessories include cut-off wheels, polishing wheels, grinding wheels, sanding discs and other cutting bits. In addition to the availability of specialized types of shaping accessories, shaping accessories may further be specifically designed for the particular type of material that is to be shaped. For example, U.S. Pat. No. 6,758,639 assigned to Credo Technology Corporation discloses a bit that is designed for use with drywall.
To cut sheetrock or drywall, a bit must be capable of first axially penetrating the drywall panel, and then making a lateral cut in the panel. The drywall bit can be used first to drill through the panel directly adjacent to an electrical outlet box, for instance. The bit is then conveyed in a direction perpendicular to the length of the bit, following the contour of the outlet box. The rotary tool is then manipulated to completely encircle the outlet box to cut the preferred opening in the drywall panel. In order to address these specific needs, the '639 patent discloses a bit with a single helical flute having a particular geometry. In one embodiment, the flute defines a cutting edge within a specific range of helix angles relative to the longitudinal axis of the bit. In another feature, the cutting edge of the flute is situated at a particular rake angle relative to the axis of the bit and the fluted portion of the bit has a web thickness that is based upon the cutting diameter of the bit.
In bits such as the bit disclosed in the '639 patent, cutting edges are defined by the junction of a flute and a land. The cutting edges penetrate the material being shaped and carve out a wedge of the material. While this mechanism is useful in relatively soft, ductile materials, it is not effective in harder and/or more brittle materials. For example, it is exceedingly difficult to cut through materials such as ceramics or hard crystalline material wherein the hardness of the material being shaped approaches the hardness of the drill bit. Likewise, it is difficult to achieve a cut that is acceptably smooth when working with brittle materials such as various types of glass.
Typically, two types of drill bits, the spear point drill bit and the core drill bit, are utilized when shaping ceramic materials. The spear point drill is shaped much like a spear point. The core drill has a hollow core with a cylindrical cutting edge surrounding the core. These bits may be modified to include a diamond abrasive on the cutting edge of the bit. While these bits are useful in boring operations such as making a hole through a material, neither bit can be used to cut along a line in the plane of the material such as to provide cutout areas in a tile.
An alternative to the bits set forth above is a frustum shaped bit with diamond grit adhered to the working portion of the bit. These bits provide the benefit of a harder abrasive material. The bits, however, do not cut through the material being shaped. Rather, the coated frustum bits grind material away from the work piece. Thus, the coated frustum bits can be used to provide cutout areas in a tile. The grinding of hard materials, however, generates a substantial amount of heat. The increased heat significantly impacts the longevity of the coated frustum bits. Additionally, the spaces between the grits tend to become blocked with dust, thereby reducing grinding capacity of the bit.
What is needed is a configuration for an accessory that reduces the problems associated with the shaping of hard or brittle materials such as tile. It would be beneficial if the accessory provided an increased rate of material removal. It would be further beneficial if the configuration of the accessory facilitated the reduction of the amount of heat generated during material removal and facilitated the dissipation of any such heat.